In motor vehicles, the engine torque is transferred to the driven wheels via the drive train, thus resulting in a certain drive torque acting on the wheels. In the case of a sufficiently high roadway friction value and a sufficiently high wheel contact force, the drive torque is converted into vehicle acceleration. If, however, the drive torque is too high in relation to the friction value, a drive slip occurs at the particular wheel and the wheel is spinning. In the most unfavorable case, it may happen that the vehicle accelerates very slowly or not at all.
For this reason, traction aid functions, such as ABD (automatic brake differential), were developed in the past which assisted with starting and accelerating of vehicles. One known specific embodiment of such a traction aid function includes, for example, a hydraulic unit which automatically builds up brake pressure during a starting operation at one or multiple slip-affected wheels to transfer the drive torque from the slip-affected wheel(s) to at least one other wheel which may apply a higher drive torque. In this way, it is possible to start and accelerate on greatly differing friction values, e.g., snow/ice on the one side of the vehicle and asphalt on the other side of the vehicle.
Such starting aid systems, however, require information regarding the wheel rotational speed of every single wheel. Every single wheel of the vehicle must thus be equipped with wheel rotational speed sensors. This is relatively complex and expensive, in particular in vehicles having more than two axles.